The present invention relates to a control system and more particularly to a control system for controlling an image array sensor having a predetermined number of pixels and controlling communication between the image array sensor and a microcontroller by way of a serial communication interface which allows various subsets of the pixels or subwindows as well as the mode of operation of the image array sensor to be efficiently and economically controlled by way of a circuit that is adapted to be formed as an application specific integrated circuit (ASIC) and even integrated with the image array sensor and the microcontroller to form a custom IC.
Image array sensors are generally known in the art. Both photogate and photodiode image array sensors are known. Examples of such image array sensors are disclosed in U.S. Pat. Nos. 5,386,128 and 5,471,515 and 2/SPIE VOL. 1900, “ACTIVE PIXEL SENSORS: ARE CCD'S DINOSAURS?” by Eric R. Fossum, pages 2-14, July 1993, hereby incorporated by reference. Active pixel image array sensors are also known, for example, as manufactured by PHOTOBIT LLC, La Crescenta, Calif. Such active pixel image array sensors are normally provided with a predetermined number of pixels forming a window, for example, a 50×50 window.
There are several important control considerations related to such active pixel image array sensors. One important consideration relates to what is commonly known as a windowing function. A windowing function relates to the ability to control the images of subwindows within the image array sensor for various purposes. For example, in the above-identified U.S. Pat. No. 5,837,994, an active pixel image array sensor is used for headlamp and tail lamp sensing as part of an automatic headlamp dimming system. That system utilizes an optical system for imaging tail lamps and headlamps on different portions of the image array sensor. More particularly, in one embodiment of the invention, the image sensor is divided up into virtually two identically sized independently positioned subwindows in one frame through different filters, one for imaging headlamps and the other for imaging tail lamps. In such an application, one row may be scanned from the first subwindow and a corresponding row from the other window. The process is repeated until all of the rows in the subwindows have been scanned.
The windowing function may also be used to control the data throughput of the system. For example, in the application discussed above, it is necessary to discriminate noise, such as road signs and street lamps. In such an application, a harmonic analysis may be used to determine if an AC power line voltage is present. In such an application, the strongest harmonic is normally 120 Hz for 60 Hz line voltage in the U.S. and a 100 Hz for 50 Hz line voltage in Europe. In order to utilize a Fourier series analysis to detect the 100 and 120 Hz frequency components, the data must be sampled at a rate, which is generally more than twice either frequency, and divides equally into 1/50 second and 1/60 second full cycle. For example, 6 uniformly spaced samples may be taken at a rate of 300 samples per second for the 50 Hz line frequency and 5 samples at the same 300 sample per second rate for a 60 Hz line frequency. The 300 sample per second rate is about 10 times the usual 30 sample per second frame rate often used for video cameras. To avoid excessively high data throughput rates, the frame size may be limited to a relatively small size, for example, as small as 2 pixels by 2 pixels.
The windowing feature can also be used for alignment of the system. For example, as discussed in the above-identified co-pending application, a useful field of view for sensing oncoming headlamps of an approaching vehicle is approximately 10° in elevation by 30° in width. However, in such a system, it is preferable to allow for some error in the optical alignment of the sensor within the vehicle. For example, a sensor with a 13° elevational field of view may be provided to allow for a 3° misalignment and still view the proper 10° elevational range. The windowing feature allows the required 10° field of view to be scanned reducing, for example, better than 20 percent of the image processing data throughput for the function. In particular, in order to obtain a proper field of view, a calibration measurement may be taken after the system is mounted. The field of view may also be based on the average position of the image of oncoming headlamps or on an average of the position of a portion of the roadway normally illuminated by the controlled vehicle's own headlamps which enables the system to dim the controlled vehicle's headlamps based upon an oncoming vehicle whose headlamps normally appear at an elevation, normally only a few degrees above the upper extent of the portion of the roadway illuminated by the controlled vehicle's own headlamps.
Another important consideration in an application utilizing an active pixel image array sensor is the ability to control the sensitivity of the device. For certain applications, for example, as disclosed in the above-mentioned co-pending application, it may be necessary to adjust the sensitivity of the system in order to avoid saturation of the image array sensor. For example, in such an application, the image of headlamps from an oncoming vehicle appears as bright spots in the field of view. If the sensitivity of the image array sensor is set too high, the particular pixels which image the headlamps will saturate so that the actual intensity cannot be determined. In such a situation, since the intensity of the headlamp image is a general indicator of the distance of an oncoming vehicle, such information is lost. Secondly, the bright image of the headlamps from an oncoming vehicle is a good indication to the system that the sensed image is from an oncoming vehicle rather than being illuminated or reflected from an object illuminated by the controlled vehicle's own headlamps.
As such, there is a need to provide improved control of the window size as well as the modes of operation for such active image array sensors. In addition to sensitivity and mode of operation adjustments, other parameters, such as the frame read repetition timing and the number of frames to be read, also need to be controlled. Thirdly, an important consideration is the ability to make such changes rather rapidly.
Another important consideration with such systems is the rather limited space for such control circuits. For example, the automatic headlamp dimming system, disclosed and described in the above-mentioned co-pending application, is preferably located in the housing which shares a mounting bracket with the rearview mirror. In such an application, space is rather limited. Moreover, as with any control circuit, it is always preferred to reduce the number of components in the circuit which normally reduces the cost considerably. For example, the active pixel image array sensors as discussed above are based on CMOS technology. Accordingly, there is a need to develop circuitry which can be integrated with the image array sensor as well as the microcontroller itself.